Insulin resistance is a characteristic feature of obesity and type 2 diabetes. The PPAR-gamma nuclear receptor is the target of Thiazolidinediones (TZDs), a class of anti-diabetic drugs known to ameliorate insulin resistance. Despite the known actions of TZDs to improve insulin sensitivity, many aspects of PPARgamma biology remain unclear. In overview, we propose to delineate the tissue specific roles of PPARgamma expression in skeletal muscle, macrophage, and adipose tissue with respect to glucose tolerance and insulin sensitivity. We have previously shown that mice heterozygous for the PPARgamma null allele (whole body) display heightened insulin sensitivity. To identify the tissue(s) responsible for conferring this heightened insulin sensitivity phenotype, we have employed the Cre-Lox system to create PPARgamma tissue specific heterozygous mice. In addition we will use these tissue specific heterozygote mice to further characterize the role of PPARgamma in 1) the regulation of NF-kappaB inflammatory pathway activation, and 2) tissue specific macrophage recruitment/activation as it relates to the pathogenesis of insulin resistance. To assess the importance of macrophage PPARgamma expression on monocyte/macrophage activation and recruitment to metabolically impaired tissues, we will withdraw bone marrow from macrophage PPARgamma null mice (MX-KO) and transplant these cells into normal wild type C57 black recipient mice (BMT). Bone marrow recipient animals, BMT:MX-KO and control WT mice will be placed on a high fat diet known to cause skeletal muscle and adipose tissue insulin resistance. We will assess whole body insulin sensitivity (glucose clamp technique) and glucose tolerance in transplanted and non-transplanted mice and correlate these findings to macrophage infiltration, activation, and tissue as well as circulating cytokine/adipokine levels. Findings from these proposed studies will provide critical information to improve our mechanistic understanding and treatment of insulin resistance and diabetes.